Coding in Code View in Visual C#

Encoding Code 39 in Visual C# Coding in Code View

If you go back to the design view and double-click on the Button control you dragged over, you will see something a little more familiar than all of this crazy markup Usually called the code-behind, this is the C# code that makes the form manageable by the server This code should look like this:

System; SystemCollectionsGeneric; SystemLinq; SystemWeb; SystemWebUI; SystemWebUIWebControls;

public partial class _Default : SystemWebUIPage { protected void Page_Load(object sender, EventArgs e) { } protected void ChangeText_Click(object sender, EventArgs e) { } }

Let s break this down a little I know you ve seen a class before, and that s all this is, but there are a few things that I want to point out: This is a partial class Partial classes are covered in Book II The rest of this class is built-in Web functionality, and it used to appear in this file Fact is, no one ever needed to edit it, so Microsoft took it out I m glad they did This is a lot easier to look at The class inherits from SystemWebUIPage The Page class provides all the tools you need to keep a collection of the controls in the page together This is very important for some Web applications, but it s a little beyond the scope of this book Read the documentation for the Page class It s an important part of ASPNET There is an event handler for PageLoad Remember the ASPNET load sequence in 1 This is why it is important You can do pre-setup operations in this handler There is an event handler for the ButtonClick event Hey, how did this get there Oh yeah, you double-clicked on the control to get the default event handler, just like I talk about in Book I Depending on your background, you might find this feels either very familiar, or very foreign This is not like the classic Active Server Pages days, or like modern PHP with inline scripting Although inline scripting is a way you can code with ASPNET, it isn t the default way If you are a Windows programmer, you will probably feel very comfortable with Web forms They work in a similar fashion However, as I mention

in 1, there is no real state management on these controls it is all faked by the ViewState variable in the HTML, and if you overuse the ViewState, you will have a slow application

Adding some functionality using C#

Let s start by making the form do something Code View basically allows the developer to write code that does something useful with the Web form Here I keep it simple, but it can get much more complex There is already an event handler for the ButtonClick event so I suggest you use that method to change the text of the Label This is a common operation in Web applications The label ID was TextToChange, so you need to add this code:

TextToChangeText = It has changed! ;

That was simple You need to know that this will be the simplest event handler that you will ever write, however They get harder Run the application by pressing <F5> (If neither of us made a mistake, it should build) Then launch the Cassini server, and then your browser should launch Click the Click Me button, and your screen should look like the one in Figure 2-4

Figure 2-4: Hey, it worked!

The first time you run the Web form in the debugger, you get a message telling you that if you want to debug this project you need to change the Web config For the purposes of this book, say Yes and move on However, remember that when you go to production, you will need to review the config and change this setting I cover it in 5 You can do even more in Code View a lot more (and more than I can cover here) The next three chapters include tips and tricks that you can absorb